Fin material made of aluminum alloy for heat exchanger

ABSTRACT

A fin material made of an aluminum alloy for heat exchangers contains 1.0 to 2.0 mass % of Mn, 0.7 to 1.4 mass % of Si, and 0.05 to 0.3 mass % of Fe, and one or more kinds of 0.05 to 0.3 mass % of Zr, 0.05 to 0.3 mass % of Cr, and 0.05 to 0.3 mass % of V, with the balance being Al and unavoidable impurities, in which a number density of intermetallic compounds having a circle-equivalent diameter of 0.025 to 0.4 μm before braze-heating is 3.0×10 6  particles/mm 2  or more, an amount of solid solution of Mn is 0.3 mass % or less and a respective amount of solid solution of Zr, Cr, and V is 0.1 mass % or less, and a recrystallization completion temperature during a temperature rise at the time of braze-heating is 450° C. or less.

TECHNICAL FIELD

The present invention relates to a fin material made of an aluminum alloy for heat exchangers preferably used as a fin material for heat exchangers such as radiators, heater cores, condensers, and intercoolers.

BACKGROUND ART

An aluminum alloy is lightweight and excellent in strength, and further, excellent in thermal conductivity, and thus has been preferably used in materials for heat exchangers such as condensers, radiators, heater cores, and intercoolers.

Such heat exchangers are conventionally assembled by braze-joining a fin of an aluminum formed in a corrugated form by corrugation forming with other members. As a fin material made of an aluminum alloy, pure aluminum based alloys excellent in thermal conductivity, such as JIS 1050 alloys, and Al—Mn based alloys excellent in strength and buckling resistance, such as JIS 3003 alloys have been generally used. In addition, a technique of preventing corrosion of a tube of a heat exchanger by electrochemically lowering the potential of a fin material in order to preferentially corrode the fin material by a sacrificial anode effect has been generally used.

In recent years, there is an increasing demand for size reduction, weight reduction, and performance enhancement of heat exchangers. Along with this demand, reducing thickness of a fin material made of an aluminum alloy has also been required. In order to realize such reduction of thickness, further strength is required to prevent deformation and buckling of a fin material during a manufacturing process of a heat exchanger.

Patent Literature 1, for example, describes a method for manufacturing a material that enhances coarsening of recrystallized grains after braze-heating to improve buckling resistance at high temperature.

PATENT LITERATURE

[Patent Literature 1] Japanese Patent Publication No. H02-115336-A

SUMMARY OF THE INVENTION Technical Problem

If a fin material is buckled and deformed before reaching a temperature of about 550 to 580° C., which is a temperature at which a filler alloy starts to melt, it may lead to non joining of the fin and other members. Therefore, in a high temperature region at the time of braze-heating, heat resistance (buckling resistance) that would not cause buckling and deformation in the fin is required.

Although Cited Literature 1 enhances coarsening of recrystallized grains after braze-heating, only a small effect is exerted with respect to deformation suppression of the fin material before a temperature at which a filler alloy melts at the time of brazing because the size of crystallized grains affects the buckling resistance of the fin only after the filler alloy is melted at a temperature of around 600° C.

Accordingly, the object of the present invention is to provide a fin material made of an aluminum alloy for heat exchangers suppressing deformation of a fin material and having superiority in sagging resistance at a range of 400° C. to 580° C., which is equal to or below a temperature at which a filler alloy melts at the time of brazing.

Solution to Problem

The inventors of the present invention conducted an intensive investigation to solve the above problem, and found out that a fin material made of an aluminum alloy for heat exchangers capable of solving the above problem can be obtained by using an aluminum alloy material having a particular component, by adjusting homogenizing treatment condition, hot rolling condition, annealing condition, and cold rolling condition, and by obtaining preferable intermetallic compound distribution and the amount of solid solution.

That is, the present invention (1) provides a fin material made of an aluminum alloy for heat exchangers, containing 1.0 to 2.0 mass % of Mn, 0.7 to 1.4 mass % of Si, and 0.05 to 0.3 mass % of Fe, and one or more kinds of 0.05 to 0.3 mass % of Zr, 0.05 to 0.3 mass % of Cr, and 0.05 to 0.3 mass % of V, with the balance being Al and unavoidable impurities, wherein

a number density of intermetallic compounds having a circle-equivalent diameter of 0.025 to 0.4 μm before braze-heating is 3.0×10⁶ particles/mm² or more,

an amount of solid solution of Mn is 0.3 mass % or less and a respective amount of solid solution of Zr, Cr, and V is 0.1 mass % or less, and

a recrystallization completion temperature during a temperature rise at the time of braze-heating is 450° C. or less.

The present invention (2) provides a fin material made of an aluminum alloy for heat exchangers (1) further containing one or more kinds of 0.5 to 4.0 mass % of Zn, 0.01 to 0.4 mass % of Cu, 0.01 to 0.3 mass % of Mg, and 0.05 to 0.3 mass % of Ti.

Advantageous Effects of Invention

The present invention provides a fin material made of an aluminum alloy for heat exchangers suppressing deformation of a fin material and having superiority in sagging resistance at a range of 400° C. to 580° C., which is equal to or below a temperature at which a filler alloy melts at the time of brazing.

DESCRIPTION OF EMBODIMENTS

A fin material made of an aluminum alloy for heat exchangers of the present invention contains 1.0 to 2.0 mass % of Mn, 0.7 to 1.4 mass % of Si, and 0.05 to 0.3 mass % of Fe, and one or more kinds of 0.05 to 0.3 mass % of Zr, 0.05 to 0.3 mass % of Cr, and 0.05 to 0.3 mass % of V, with the balance being Al and unavoidable impurities, wherein

a number density of intermetallic compounds having a circle-equivalent diameter of 0.025 to 0.4 μm before braze-heating is 3.0×10⁶ particles/mm² or more,

an amount of solid solution of Mn is 0.3 mass % or less and a respective amount of solid solution of Zr, Cr, and V is 0.1 mass % or less, and

a recrystallization completion temperature during a temperature rise at the time of braze-heating is 450° C. or less.

The fin material made of an aluminum alloy for heat exchangers of the present invention contains Mn, Si, and Fe, and one or more kinds of Zr, Cr, and V, with the balance being Al and unavoidable impurities. The fin material made of an aluminum alloy for heat exchangers of the present invention may include unavoidable impurities of 0.05 mass % or less respectively, and 0.15 mass % or less in total.

The content of Mn in an aluminum alloy according to the fin material made of an aluminum alloy for heat exchangers of the present invention is 1.0 to 2.0 mass %, and preferably 1.2 to 1.8 mass %. Mn is an essential element for enhancing the strength in a temperature range of 400° C. to 580° C. before the filler alloy melts at the time of brazing. Mn generates Al—Mn—Si (—Fe) based intermetallic compounds together with Si, contributes to dispersion strengthening, and improves material strength at high temperature. If the content of Mn in the aluminum alloy is below the above range, the effects are not exerted sufficiently. If the content of Mn in the aluminum alloy exceeds the above range, coarse intermetallic compounds are generated at the time of casting, rolling property is degraded, and manufacturing of a sheet material becomes difficult.

The content of Si in the aluminum alloy according to the fin material made of an aluminum alloy for heat exchangers of the present invention is 0.70 to 1.4 mass %, and preferably 0.85 to 1.3 mass %. Si is an essential element for enhancing the strength in a temperature range of 400 to 580° C. before the filler alloy melts at the time of brazing. Si generates Al—Mn—Si (—Fe) based intermetallic compounds together with Al, contributes to dispersion strengthening, and improves material strength at high temperature. If the content of Si in the aluminum alloy is below the above range, the effects are not exerted sufficiently. If the content of Si in the aluminum alloy exceeds the above range, the amount of solid solution of Si increases and the melting point decreases, and may be susceptible to melting of a fin material due to excessive brazing erosion at the time of braze-heating.

The content of Fe in the aluminum alloy according to the fin material made of an aluminum alloy for heat exchangers of the present invention is 0.05 to 0.3 mass %, and preferably more than 0.1 mass % and 0.3 mass % or less. If the content of Fe in an aluminum alloy exceeds the above range, a large number of coarse crystallized products (intermetallic compounds) generated at the time of casting are generated, and as a result, precipitation of fine intermetallic compounds is decreased. Accordingly, a desired strength cannot be obtained in a temperature range of 400 to 580° C., and also, self-corrosion resistance of the fin material may be degraded because the crystallized products (intermetallic compounds) generated at the time of casting become a corrosion starting point. If the content of Fe in an aluminum alloy is below 0.05 mass %, the amount of solid solution of Mn increases and the melting point decreases, and may be susceptible to melting of the fin material due to brazing erosion at the time of braze-heating. In addition, it causes increase in cost because high-purity aluminum metal needs to be used.

The aluminum alloy of the fin material made of an aluminum alloy for heat exchangers of the present invention contains, in addition to Mn, Si, and Fe, one or more kinds of Zr, Cr, and V.

If the aluminum alloy according to the fin material made of an aluminum alloy for heat exchangers of the present invention includes Zr, the content of Zr is 0.05 to 0.3 mass %, and preferably 0.1 to 0.2 mass %. Zr precipitates as Al—Zr based intermetallic compounds, and enhances deformation resistance at high temperature. If the content of Zr is below the above range, such effects cannot be obtained. If the content of Zr exceeds the above range, it becomes susceptible to form huge intermetallic compounds, and lowers plastic workability.

If the aluminum alloy according to the fin material made of an aluminum alloy for heat exchangers of the present invention includes Cr, the content of Cr is 0.05 to 0.3 mass %, and preferably 0.1 to 0.2 mass %. Cr precipitates as Al—Cr based intermetallic compounds, and enhances deformation resistance at high temperature. If the content of Cr is below the above range, such effects cannot be obtained. If the content of Cr exceeds the above range, it becomes susceptible to form huge intermetallic compounds, and lowers plastic workability.

If the aluminum alloy according to the fin material made of an aluminum alloy for heat exchangers of the present invention includes V, the content of V is 0.05 to 0.3 mass %, and preferably 0.1 to 0.2 mass %. V precipitates as Al—V based intermetallic compounds, and enhances deformation resistance at high temperature. If the content of V is below the above range, such effects cannot be obtained. If the content of V exceeds the above range, it becomes susceptible to form huge intermetallic compounds, and lowers plastic workability.

In the aluminum alloy according to the fin material made of an aluminum alloy for heat exchangers of the present invention, the amount of solid solution of Mn is 0.3 mass % or less, and the respective amount of solid solution of Zr, Cr, and V is 0.1 mass % or less. If the amount of solid solution of Mn exceeds 0.3 mass %, recrystallization is delayed due to precipitation of intermetallic compounds during braze-heating, and leads to degradation of sagging resistance. If the amount of solid solution of Zr exceeds 0.1 mass %, recrystallization is delayed due to precipitation of Al—Zr based intermetallic compounds during braze-heating, and leads to degradation of sagging resistance. If the amount of solid solution of Cr exceeds 0.1 mass %, recrystallization is delayed due to precipitation of Al—Cr based intermetallic compounds during braze-heating, and leads to degradation of sagging resistance. If the amount of solid solution of V exceeds 0.1 mass %, recrystallization is delayed due to precipitation of Al—V based intermetallic compounds during braze-heating, and leads to degradation of sagging resistance. “The respective amount of solid solution of Zr, Cr, and V is 0.1 mass % or less” indicates that: if the aluminum alloy according to the fin material made of an aluminum alloy for heat exchangers of the present invention includes only Zr among Zr, Cr, and V, the amount of solid solution of Zr is 0.1 mass % or less, if the aluminum alloy includes only Cr among Zr, Cr, and V, the amount of solid solution of Cr is 0.1 mass % or less, if the aluminum alloy includes only V among Zr, Cr, and V, the amount of solid solution of V is 0.1 mass % or less, if the aluminum alloy includes Zr and Cr among Zr, Cr, and V, the amount of solid solution of Zr is 0.1 mass % or less and the amount of solid solution of Cr is 0.1 mass % or less, if the aluminum alloy includes Zr and V among Zr, Cr, and V, the amount of solid solution of Zr is 0.1 mass % or less and the amount of solid solution of V is 0.1 mass % or less, if the aluminum alloy includes Cr and V among Zr, Cr, and V, the amount of solid solution of Cr is 0.1 mass % or less and the amount of solid solution of V is 0.1 mass % or less, if the aluminum alloy includes Zr, Cr, and V among Zr, Cr, and V, the amount of solid solution of Zr is 0.1 mass % or less, the amount of solid solution of C is 0.1 mass % or less and the amount of solid solution of V is 0.1 mass % or less.

The aluminum alloy according to the fin material made of an aluminum alloy for heat exchangers of the present invention may further contain one or more kinds of 0.5 to 4.0 mass % of Zn, 0.01 to 0.4 mass % of Cu, 0.01 to 0.3 mass % of Mg, and 0.05 to 0.3 mass % of Ti.

The aluminum alloy according to the fin material made of an aluminum alloy for heat exchangers of the present invention may further contain 0.5 to 4.0 mass % of Zn. Zn provides a sacrificial anode effect by lowering the potential of the fin material. If the content of Zn in the aluminum alloy is below the above range, the effects will not be exerted sufficiently. If the content of Zn exceeds the above range, self-corrosion resistance of the fin material may be degraded.

The aluminum alloy according to the fin material made of an aluminum alloy for heat exchangers of the present invention may further contain 0.01 to 0.40 mass % of Cu. Cu has a function of enhancing the strength at high temperature of the fin material by solid-solution strengthening. If the content of Cu in the aluminum alloy is below the above range, the effects will not be exerted sufficiently. If the content of Cu exceeds the above range, the potential of the fin material becomes high, and a sacrificial anode effect may be degraded.

The aluminum alloy according to the fin material made of an aluminum alloy for heat exchangers of the present invention may further contain 0.01 to 0.30 mass % of Mg. Mg has a function of enhancing the strength at high temperature of the fin material by solid-solution strengthening. If the content of Mg is below 0.01 mass %, the effects will not be exerted sufficiently. If the content of Mg exceeds 0.30 mass %, brazing failure may occur due to reaction with a flux.

The aluminum alloy according to the fin material made of an aluminum alloy for heat exchangers of the present invention may further contain 0.05 to 0.30 mass % of Ti, and preferably 0.1 to 0.2 mass % of Ti. Ti enhances the strength by solid-solution strengthening. If the content of Ti in the aluminum alloy is below the above range, such effects may not be obtained. If the content of Ti exceeds the above range, it becomes susceptible to form huge intermetallic compounds, and lowers plastic workability.

In the aluminum alloy according to the fin material made of an aluminum alloy for heat exchangers of the present invention, a number density of intermetallic compounds having a circle-equivalent diameter of 0.025 to 0.4 μm is 3.0×10⁶ particles/mm² or more, preferably 3.8×10⁶ particles/mm² or more, and more preferably 4.0×10⁶ particles/mm² or more.

Although dispersion strengthening and solid solution-strengthening are considered to enhance high-temperature strength during braze-heating, the inventors of the present invention found out that high-temperature strength can be enhanced by ensuring dense intermetallic compounds having large contribution to dispersion strengthening at high temperature during braze-heating. Although a part of intermetallic compounds (Al—Mn—Si (—Fe) and Al—Zr based, Al—Cr based, and Al—V based compounds) is solid-dissolved during braze-heating, the distribution of intermetallic compounds remaining during braze-heating is based on the distribution of intermetallic compounds before braze-heating. Thus, a material in which intermetallic compounds are densely dispersed before braze-heating has the distribution of intermetallic compound remaining during braze-heating densely dispersed, and contributes to enhancing high-temperature strength. The inventors of the present invention found out that, if the number density of intermetallic compounds having a circle-equivalent diameter of 0.025 to 0.4 μm is below the above range, precipitates at high temperature during braze-heating are small, the effect of dispersion strengthening is insufficient, and sufficient high-temperature strength cannot be ensured during braze-heating. The higher the number density of the intermetallic compounds described above is, the higher the density of remaining intermetallic compounds is, and results in enhanced high-temperature strength. Accordingly, although the upper limit of the number density of intermetallic compounds having a circle-equivalent diameter of 0.025 to 0.4 μm is not particularly limited, it is normally 2.0×10⁷ particles/mm² or less.

In the fin material of an aluminum alloy for heat exchangers of the present invention, a recrystallization completion temperature during a temperature rise at the time of braze-heating is 450° C. or less, and preferably 400° C. or less. When a worked structure of the fin material is recovered and recrystallized during braze-heating, deformation may occur due to diffusion of vacancies through dislocation and the like. If the recrystallization completion temperature exceeds the above range, the deformation of the fin material accompanied by the recrystallization described above becomes remarkable, and lowers sagging resistance during braze-heating.

In order to make the recrystallization completion temperature to be 450° C. or less during a temperature rise at the time of braze-heating, the amount of solid solution of Mn is made 0.3 mass % or less, and preferably 0.2 mass % or less in the aluminum alloy according to the fin material made of an aluminum alloy for heat exchangers of the present invention. If the amount of solid solution of Mn exceeds 0.3 mass %, recrystallization may be delayed due to precipitation of Al—Mn—Si (—Fe) based intermetallic compounds during braze-heating. The amount of solid solution of Zr is made 0.1 mass % or less. If the amount of solid solution of Zr exceeds 0.1 mass %, recrystallization may be delayed due to precipitation of Al—Zr based intermetallic compounds during braze-heating. The amount of solid solution of Cr is made 0.1 mass % or less. If the amount of solid solution of Cr exceeds 0.1 mass %, recrystallization may be delayed due to precipitation of Al—Cr based intermetallic compounds during braze-heating. The amount of solid solution of V is made 0.1 mass % or less. If the amount of solid solution of V exceeds 0.1 mass %, recrystallization may be delayed due to precipitation of Al—V based intermetallic compounds during braze-heating.

In the fin material made of an aluminum alloy for heat exchangers of the present invention, the number density of intermetallic compounds having a circle-equivalent diameter of 0.025 to 0.4 μm before braze-heating and the amount of solid solution of Mn, Zr, Cr, and V are determined mainly in the processes from casting to hot rolling and in the subsequent process of annealing. Accordingly, in order to improve material strength at high temperature during braze-heating, it is necessary to control the conditions of these processes, and make the number density of intermetallic compounds having a circle-equivalent diameter of 0.025 to 0.4 μm before braze-heating and the amount of solid solution of Mn, Zr, Cr, and V to be within the range of the present invention.

In regard to a method of manufacturing a fin material made of an aluminum alloy for heat exchangers of the present invention, first, an ingot is produced by casting a molten aluminum alloy so as to correspond to the above described composition. Then, in order to provide excellent high temperature and buckling resistance, it is preferable to suppress the precipitation of coarse intermetallic compounds, and not to perform homogenization treatment with respect to the ingot obtained by casting from the point of view of increasing the number density.

Next, the ingot obtained by casting is hot rolled. At this time, in order to ultimately obtain an aluminum alloy having the number density of intermetallic compounds having a circle-equivalent diameter of 0.025 to 0.4 μm of 3.0×10⁶ particles/mm² or more, preferably 3.8×10⁶ particles/mm² or more, and more preferably 4.0×10⁶ particles/mm² or more, and the amount of solid solution of Mn of 0.3 mass % or less and the respective amount of solid solution of Zr, Cr, and V of 0.1 mass % or less, it is preferable to make the range of heating temperature before hot rolling to be 380 to 480° C., and more preferably 400 to 460° C. If the heating temperature before hot rolling exceeds the above range, the precipitated intermetallic compounds become coarse, sufficient dispersion strength by intermetallic compounds cannot be obtained during braze-heating, and high-temperature strength becomes degraded. If the heating temperature before hot rolling is below the above range, since hot strength of the material at the time of rolling is high, a high power hot-rolling mill becomes necessary, and also, rolling becomes difficult due to excessive ear cracking at the time of rolling. Then, although the hot rolling is started at the heating temperature before hot rolling described above, it is preferable to make the temperature of the hot rolled sheet to be 360 to 480° C. in the hot rolling stage until the total rolling ratio reaches 50% after starting the hot rolling. Processing, recovering, and recrystallization in the rolled sheet occur consecutively during hot rolling and promote precipitation of intermetallic compounds on a subgrain boundary formed in the process of recovering. If the temperature of hot rolled sheet in the hot rolling stage exceeds the above range, intermetallic compounds grow and the number density becomes low, and a predetermined density of intermetallic compounds will not be obtained, resulting in lowering of material strength at high temperature. If the temperature is below the above range, the precipitation itself of intermetallic compounds becomes small, and also, the amount of solid solution of Mn, Zr, Cr, and V becomes excessive, and a predetermined number density of intermetallic compounds and a predetermined amount of solid solution will not be obtained.

Next, the hot rolled sheet obtained by hot rolling is cold rolled. In the cold rolling, intermediate annealing may be performed once or twice in total until reaching the final sheet thickness, or final annealing may be performed after the final cold rolling. The annealing temperature during that time is preferably 100 to 280° C. If the annealing temperature exceeds the above range, the precipitated intermetallic compounds become coarse, and the number density becomes small. Accordingly, in the temperature range of 400 to 580° C. before the filler alloy melts during brazing, sufficient dispersion strength by intermetallic compounds cannot be obtained, and the material strength degrades. If the annealing temperature is below the above range, the effect of annealing is not obtained, and is uneconomical.

The fin material made of an aluminum alloy for heat exchangers of the present invention is preferably used as a fin for heat exchangers. For example, the fin material made of an aluminum alloy for heat exchangers of the present invention is, after being formed into a fin shape by corrugation forming, assembled with heat exchanger members such as a flow passage forming part, a header plate, and the like, and is subjected to braze-heating, thereby obtaining a heat exchanger.

The above heat exchanger is assembled by arranging the fin material to an outer surface of the flow passage forming part in which both end parts are attached to the header plate. Next, the superimposed parts of both ends of the flow passage forming part, the fin material and the outer surface of the flow passage forming part, and both ends of the flow passage forming part and the header plate are joined simultaneously by a single braze-heating. The method of brazing may be brazing without flux, Nocolok brazing, and vacuum brazing.

Examples

Next, the present invention will be described in more details based on the examples of the present invention and comparative examples, but the invention is not intended to be limited thereto.

Aluminum alloys having chemical compositions shown in Table 1 were melted by an ordinary method, ingots were formed by semi-continuous casting, and both faces thereof were faced and finished. The thickness of each of the faced ingots was 400 mm. These ingots of aluminum alloys were not subjected to homogenizing treatment, and subjected to heating with the retention time of 6 hours at a temperature shown in Table 2 before hot rolling. Then, hot rolling was started at that temperature, and hot rolling was performed up to ultimately having a thickness of 3.0 mm under a condition shown in Table 2. Thereafter, cold rolling was performed, and, in the course thereof, subjected to intermediate annealing with the retention time of 3 hours at a temperature shown in Table 2. Then, cold-finish rolling was performed, and a fin material having a sheet thickness of 0.07 mm was obtained. The present invention is not limited to the sheet thickness of the final sheet of the present example. The thickness of the final sheet is generally around 0.03 to 0.10 mm.

TABLE 1 Alloy Chemical compositions (mass %) No. Mn Si Fe Zr Cr V Zn Cu Mg Ti Example 1 1.5 1.0 0.15 0.2 — — 1.5 — — — 2 1.4 1.4 0.2 — 0.2 — 4.0 — 2.0 — 3 1.3 0.7 0.15 — — 0.1 1.0 — — — 4 2.0 1.0 0.15 0.1 0.1 — 0.5 0.20 — — 5 1.0 1.3 0.15 — — 0.2 2.0 — 0.10 — 6 1.6 1.2 0.1 0.3  0.05 — 1.0 — — — 7 1.2 1.0 0.2  0.05 — 0.3 2.0 — — — 8 1.4 1.0 0.15 — 0.3  0.05 1.0 — — — 9 1.2 0.9 0.2 — 0.1 — — — 0.30 0.05 10 1.4 1.2 0.05 0.2 — — 0.5 — 0.10 — 11 1.6 1.3 0.12 — — 0.2 4.0 — — — 12 1.6 0.85 0.2 — 0.1 0.1 0.5 0.30 — — 13 1.8 1.2 0.2 — 0.2 — 1.0 0.10 — — 14 1.2 1.1 0.15 0.1 — — 3.0 — 0.10 0.30 15 1.4 1.2 0.3 — 0.2 — 0.5 0.01 — — 16 1.6 1.1 0.2 — — 0.1 2.0 0.40 0.05 — Comparative 17 2.4 1.2 0.2 — 0.2 — — — — — Example 18 0.7 0.9 0.2 — 0.2 — 1.0 — — — 19 1.4 1.6 0.15 0.1 — — 1.0 — — — 20 1.2 0.6 0.2 — — 0.1 2.0 — — — 21 1.4 1.2 0.5 — — 0.2 1.0 — — — 22 1.6 1.3 0.02 0.2 — — 2.0 — — — 23 1.2 1.3 0.2 0.4 — — 1.0 — — — 24 1.4 1.6 0.15 — 0.4 — 1.0 — — — 25 1.2 1.0 0.2 — — 0.4 3.0 — — — 26 1.4 0.9 0.2 — 0.1 — 0.5 — — 0.4  27 1.6 1.1 0.12 0.1 — — 4.5 — — — 28 1.2 1.3 0.2 0.1 — — 2.0 0.6  — — 29 1.4 1.0 0.3 — — 0.1 2.0 — 0.4  —

TABLE 2 Hot rolling condition Heating Temperature of hot temperature rolled sheet at the Intermediate Example Alloy Homogenizing before hot time of reaching sheet annealing heating No. No. treatment rolling thickness of 28 mm (° C.) temperature (° C.) Example 1 1 none 440 400 180 2 2 none 440 400 180 3 3 none 400 380 180 4 4 none 420 380 180 5 5 none 420 380 180 6 6 none 460 400 180 7 7 none 440 380 140 8 8 none 380 360 180 9 9 none 480 420 160 10 10 none 480 440 200 11 11 none 460 420 180 12 12 none 460 420 180 13 13 none 400 360 180 14 14 none 440 400 180 15 15 none 480 440 160 16 16 none 440 400 180 17 1 none 480 440 180 18 1 none 420 400 180 19 1 none 380 360 180 20 9 none 440 400 180 21 10 none 380 360 180 22 11 none 440 400 160 23 12 none 420 380 180 24 13 none 440 400 180 25 14 none 460 420 160 26 16 none 460 420 160 Comparative 27 1 500° C. × 10 hr 440 400 200 Example 28 11 none 500 440 220 29 6 none 400 320 140 30 2 none 380 320 180 31 5 none 400 320 180 32 9 none 460 400 320 33 1 none 360 Cancelled during hot rolling 34 17 none 460 Cancelled during hot rolling 35 18 none 400 360 160 36 19 none 440 400 180 37 20 none 420 400 140 38 21 none 400 380 220 39 22 none 440 390 140 40 23 none 460 420 Cancelled during cold rolling 41 24 none 460 410 Cancelled during cold rolling 42 25 none 460 420 Cancelled during cold rolling 43 26 none 460 410 Cancelled during cold rolling 44 27 none 400 370 180 45 28 none 440 400 220 46 29 none 440 400 180

The number density of intermetallic compounds before braze-heating and the amount of solid solution of Mn were measured with respect to the fin material obtained as described above. As the characteristics during braze-heating, by a tensile test of the material heated up to 400° C., whether recrystallization of the fin material at the time of reaching 400° C. during braze-heating was completed or not was confirmed, and the amount of drooping of the fin material up to 550° C. was measured by a sagging test. In addition, a brazability test and a corrosion resistance test were performed. The results of these are shown in Table 3 and Table 4.

1. The Density of Intermetallic Compounds Before Braze-Heating

A field emission-scanning electron microscopy (FE-SEM) was used for the measurement. Compounds on a surface of a fin material sample were observed, and the number density of intermetallic compounds having a predetermined circle-equivalent diameter was measured by image analysis. Specifically, twenty viewing fields were observed with a magnification of 20,000, and the number density of intermetallic compounds having a circle-equivalent diameter of 0.025 μm to 0.4 μm was calculated after a binarizing process.

2. Tensile Strength of the Fin at 500° C.

A fin material sample before braze-heating was formed in a JIS No. 13 B tensile test piece, and the tensile strength was measured at 500° C. by a tensile testing machine. A temperature elevation rate of the fin material up to 500° C. was 100° C./min. Then, after the fin material reached 500° C., a tensile test was performed at a tensile speed of 2 mm/minute, while the temperature was retained. The tensile strength was read from the obtained stress-strain curve. If the tensile strength was 17 MPa or more, the result was indicated as “⊙”, if the tensile strength was 15 MPa or more to below 17 MPa, the result was indicated as “◯”, and if the tensile strength was below 15 MPa, the result was indicated as “x”.

3. The Amount of Solid Solution of Mn, Zr, Cr, and V Before Braze-Heating

A fin material before braze-heating was dissolved in a phenol solution, the undissolved intermetallic compounds were removed by filtration, subjected to emission analysis, and the amount of solid solution of Mn, Zr, Cr, and V was measured.

4. Tensile Test at a Room Temperature after Heating Up to 400° C.

The fin material was heated up to 400° C. at a temperature evaluation rate of 100° C./min, and subjected to a tensile test in accordance with JIS Z2241, under conditions of a tensile speed of 10 mm/minute and a gauge length of 50 mm at a room temperature. 0.2% proof stress was read from the obtained stress-strain curve. The recrystallization was determined to be completed if the value was 80 MPa or less, and indicated as success (◯). The recrystallization was determined to be incomplete if the value exceeded 80 MPa, and was indicated as failure (x).

5. The Amount of Drooping of the Fin at 550° C.

Each fin material was cut into a size having a width of 10 mm and a length of 55 mm. A portion at a length of 40 mm was projected in a non-supported state, and the remaining 15-mm portion was heated up to 580° C. in a state horizontally held by a jig. The temperature elevation rate of the fin material up to 550° C. was 100° C./min. After heating, the amount of drooping of the edge of the projected portion of the fin material was measured. If the amount was 15 mm or less, the result was indicated as “⊙”, if the amount exceeded 15 mm and was 18 mm or less, the result was indicated as “◯”, and if the amount exceeded 18 mm, the result was indicated as “x”.

6. Brazability Test

Each fin material was subjected to corrugation forming, and a miniature core was manufactured by assembling with a tube material having a thickness of 0.25 mm using JIS A3003 alloys as a core material and JIS A4045 alloys as a skin material (filler alloy, cladding rate of 10%). A fluoride-based flux having a concentration of 3% was applied, heated for 3 minutes at 600° C. in a nitrogen gas atmosphere, and brazing was performed. Next, each braze-joined fin material was physically removed from the tube material by a cutter blade, and a trace of a fin joining part remaining on the surface of the tube material was observed. Then, the number of non-joining portions (portions in which no trace of joining parts remained after brazing) was counted, and a joining ratio based on the following formula was obtained. A joining ratio of 90% or more was indicated as “◯”, and a joining ratio of below 90% was indicated as “x”.

Joining ratio (%)=(1−the number of non-joining portions/the number of entire joining portions)×100

-   -   The number of entire joining portions: The number of entire         brazing portions     -   The number of non-joining portions: The number of portions in         which no trace of joining parts remained after brazing

Furthermore, every fifty portions of the cross section of the joining parts of the fin material of the braze-joined miniature core and the tube were observed, and the number of portions in which half or more of the thickness of the fin material was melted was counted, and a fin melting ratio based on the following formula was obtained.

Fin melting ratio (%)=(the number of joining portions in which half or more of the thickness of the fin material was melted/the number of observed joining portions)×100

A fin melting ratio of 10% or less was indicated as “⊙”, a fin melting ratio exceeding 10% and 20% or less was indicated as “◯”, and a fin melting ratio exceeding 20% was indicated as “x”.

7. Corrosion Resistance Test

A miniature core of a heat exchanger manufactured similarly to the case of the brazing test was subjected to a CASS test for 1 month according to JIS H8681, a corrosion state of the fin material and the tube material was investigated, and the corrosion resistance was evaluated. Quality of the corrosion resistance was evaluated as follows. If the tube material had no through holes, it was evaluated as ◯: good. If the tube material had through holes and the self-corrosion of the fin material was large, it was evaluated as x: poor.

TABLE 3 Density of intermetallic compounds Amount of solid Amount of solid Amount of solid Amount of solid having a circle-equivalent diameter of solution of Mn solution of Zr solution of Cr solution of V Example Alloy 0.025 to 0.4 μm before braze-heating: before braze- before braze- before braze- before braze- No. No. D (particles/mm²) heating mass % heating mass % heating mass % heating mass % Example 1 1 6.1 × l0⁶ 0.09 0.03 — — 2 2 5.2 × 10⁶ 0.15 — 0.04 — 3 3 4.0 × 10⁶ 0.22 — — 0.04 4 4 6.6 × 10⁶ 0.19 0.03 0.02 — 5 5 4.1 × 10⁶ 0.21 — — 0.07 6 6 6.3 × 10⁶ 0.10 0.06 0.02 — 7 7 5.3 × 10⁶ 0.13 0.01 — 0.07 8 8 3.8 × 10⁶ 0.21 — 0.09 0.03 9 9 4.7 × 10⁶ 0.18 — 0.04 — 10 10 6.0 × 10⁶ 0.12 0.04 — — 11 11 3.9 × 10⁶ 0.26 — — 0.06 12 12 3.5 × 10⁶ 0.28 — 0.06 0.06 13 13 3.9 × 10⁶ 0.28 — 0.08 — 14 14 4.7 × 10⁶ 0.14 0.03 — — 15 15 6.1 × 10⁶ 0.11 — 0.04 — 16 16 5.6 × 10⁶ 0.18 — — 0.03 17 1 3.3 × 10⁶ 0.28 0.08 — — 18 1 5.8 × 10⁶ 0.11 0.04 — — 19 1 3.8 × 10⁶ 0.26 0.06 — — 20 9 5.0 × 10⁶ 0.17 — 0.04 — 21 10 3.7 × 10⁶ 0.23 0.07 — — 22 11 6.3 × 10⁶ 0.09 — — 0.04 23 12 6.0 × 10⁶ 0.13 — 0.03 0.02 24 13 7.1 × 10⁶ 0.08 — 0.02 — 25 14 4.5 × 10⁶ 0.19 0.03 — — 26 16 6.2 × 10⁶ 0.10 — — 0.03 Comparative 27 1 1.5 × 10⁶ 0.28 0.08 — — Example 28 11 1.8 × 10⁶ 0.24 — 0.06 — 29 6 3.3 × 10⁶ 0.26 0.14 0.03 — 30 2 3.0 × 10⁶ 0.21 — 0.11 — 31 5 3.1 × 10⁶ 0.19 — — 0.12 32 9 2.6 × 10⁶ 0.25 — 0.05 — 33 1 No measurement because hot rolling was not possible 34 17 No measurement because hot rolling was not possible 35 18 2.4 × 10⁶ 0.09 — 0.08 — 36 19 4.3 × 10⁶ 0.14 0.04 — — 37 20 3.0 × 10⁶ 0.34 — — 0.04 38 21 2.8 × 10⁶ 0.26 — — 0.06 39 22 3.8 × 10⁶ 0.36 0.08 — — 40 23 No measurement due to occurrence of cracking during cold rolling 41 24 No measurement due to occurrence of cracking during cold rolling 42 25 No measurement due to occurrence of cracking during cold rolling 43 26 No measurement due to occurrence of cracking during cold rolling 44 27 5.0 × 10⁶ 0.14 0.04 — — 45 28 4.1 × 10⁶ 0.14 0.04 — — 46 29 4.6 × 10⁶ 0.12 — — 0.04

TABLE 4 Recrystallization Sagging test Miniature core brazing evaluation Example Alloy completion Amount of drooping Brazability Fin melting Corrosion No. No. temperature up to 550° C. (%) ratio (%) resistance Example 1 1 ◯ 8 ⊙ 100 ◯ 4 ⊙ ◯ 2 2 ◯ 10 ⊙ 98 ◯ 10 ⊙ ◯ 3 3 ◯ 15 ⊙ 100 ◯ 6 ⊙ ◯ 4 4 ◯ 8 ⊙ 100 ◯ 2 ⊙ ◯ 5 5 ◯ 15 ⊙ 98 ◯ 8 ⊙ ◯ 6 6 ◯ 8 ⊙ 100 ◯ 4 ⊙ ◯ 7 7 ◯ 10 ⊙ 100 ◯ 4 ⊙ ◯ 8 8 ◯ 16 ◯ 100 ◯ 4 ⊙ ◯ 9 9 ◯ 14 ⊙ 95 ◯ 2 ⊙ ◯ 10 10 ◯ 9 ⊙ 97 ◯ 14 ◯ ◯ 11 11 ◯ 16 ◯ 100 ◯ 6 ⊙ ◯ 12 12 ◯ 17 ◯ 100 ◯ 2 ⊙ ◯ 13 13 ◯ 16 ◯ 100 ◯ 4 ⊙ ◯ 14 14 ◯ 13 ⊙ 100 ◯ 4 ⊙ ◯ 15 15 ◯ 10 ⊙ 100 ◯ 4 ⊙ ◯ 16 16 ◯ 11 ⊙ 100 ◯ 4 ⊙ ◯ 17 1 ◯ 18 ◯ 100 ◯ 4 ⊙ ◯ 18 1 ◯ 14 ⊙ 100 ◯ 4 ⊙ ◯ 19 1 ◯ 17 ◯ 100 ◯ 4 ⊙ ◯ 20 9 ◯ 11 ⊙ 96 ◯ 2 ⊙ ◯ 21 10 ◯ 17 ◯ 98 ◯ 14 ◯ ◯ 22 11 ◯ 8 ⊙ 100 ◯ 6 ⊙ ◯ 23 12 ◯ 9 ⊙ 100 ◯ 2 ⊙ ◯ 24 13 ◯ 13 ⊙ 100 ◯ 4 ⊙ ◯ 25 14 ◯ 15 ⊙ 100 ◯ 4 ⊙ ◯ 26 16 ◯ 9 ⊙ 99 ◯ 2 ⊙ ◯ Comparative 27 1 ◯ 24 X 100 ◯ 4 ⊙ ◯ Example 28 11 ◯ 23 X 100 ◯ 4 ⊙ ◯ 29 6 X 32 X 97 ◯ 2 ⊙ ◯ 30 2 X 29 X 95 ◯ 4 ⊙ ◯ 31 5 X 28 X 96 ◯ 4 ⊙ ◯ 32 9 ◯ 22 X 95 ◯ 2 ⊙ ◯ 33 1 No measurement because hot rolling was not possible 34 17 No measurement because hot rolling was not possible 35 18 ◯ 23 X 100 ◯ 4 ⊙ ◯ 36 19 ◯ 16 ◯ 94 ◯ 32 X ◯ 37 20 X 33 X 100 ◯ 22 X ◯ 38 21 ◯ 23 X 100 ◯ 4 ⊙ X 39 22 X 29 X 96 ◯ 26 X ◯ 40 23 No measurement due to occurrence of cracking during cold rolling 41 24 No measurement due to occurrence of cracking during cold rolling 42 25 No measurement due to occurrence of cracking during cold rolling 43 26 No measurement due to occurrence of cracking during cold rolling 44 27 ◯ 13 ⊙ 100 ◯ 12 ◯ X 45 28 ◯ 15 ⊙ 100 ◯ 24 X X 46 29 ◯ 14 ⊙ 82 X 16 ◯ ◯

Examples 1 to 26 satisfied the conditions stipulated in the present invention, and the amount of drooping of the fin material was successful at 550° C. Brazing property and corrosion resistance were also successful.

In Comparative Examples 27 and 28, the homogenizing treatment condition and the hot rolling condition were not adequate, and the precipitated intermetallic compounds were coarse and the number density of intermetallic compounds having a circle-equivalent diameter of 0.025 to 0.4 μm was below 3.0 particles/μm². Accordingly, the amount of drooping of the fin material at 550° C. resulted in failure.

In Comparative Example 29, the hot rolling condition was not adequate, the amount of solid solution of Zr before braze-heating exceeded 0.1 mass %, and the recrystallization during braze-heating was not completed at 450° C. Accordingly, the amount of drooping of the fin material at 550° C. resulted in failure.

In Comparative Example 30, the hot rolling condition was not adequate, the amount of solid solution of Cr before braze-heating exceeded 0.1 mass %, and the recrystallization during braze-heating was not completed at 450° C. Accordingly, the amount of drooping of the fin material at 550° C. resulted in failure.

In Comparative Example 31, the hot rolling condition was not adequate, the amount of solid solution of V before braze-heating exceeded 0.1 mass %, and the recrystallization during braze-heating was not completed at 450° C. Accordingly, the amount of drooping of the fin material at 550° C. resulted in failure.

In Comparative Example 32, the annealing condition was not adequate, the precipitated intermetallic compounds were coarse, and the number density of intermetallic compounds having a circle-equivalent diameter of 0.025 to 0.4 μm was below 3.0 particles/μm². Accordingly, the amount of drooping of the fin material at 550° C. resulted in failure.

In Comparative Example 33, the heating temperature before hot rolling was low at 360° C., the hot strength of the material at the time of rolling was high, the cracking occurred during rolling, and resulted in not being able to be manufactured.

In Comparative Example 34, since the components of Mn in the fin material were excessive, the cracking occurred during rolling, and resulted in not being able to be manufactured.

In Comparative Example 35, since the components of Mn in the fin material were insufficient, the number density of intermetallic compounds having a circle-equivalent diameter of 0.025 to 0.4 μm was below 3.0 particles/μm². Accordingly, the tensile strength at 500° C. resulted in failure.

In Comparative Example 36, since the components of Si in the fin material were excessive, the melting of the fin was remarkable in the brazing test, and resulted in failure.

In Comparative Example 37, since the components of Si in the fin material were insufficient, the amount of solid solution of Mn before braze-heating exceeded 0.3 mass % and recrystallization during braze-heating was not completed at 450° C. Accordingly, the amount of drooping of the fin material at 550° C. resulted in failure. Furthermore, as a result of increase in the amount of solid solution of Mn and the like and decrease in the solidus temperature of the fin material, melting of the fin in the brazability test was remarkable, and resulted in failure.

In Comparative Example 38, since the components of Fe in the fin material were excessive, the number density of intermetallic compounds having a circle-equivalent diameter of 0.025 to 0.4 μm was below 3.0 particles/μm², and the tensile strength at 500° C. resulted in failure. In the corrosion resistance evaluation, corrosion of the fin material was remarkable, and resulted in failure.

In Comparative Example 39, since the components of Fe in the fin material were insufficient, the amount of solid solution of Mn before braze-heating exceeded 0.3 mass %, and recrystallization during braze-heating was not completed at 450° C. Accordingly, the amount of drooping of the fin material at 550° C. resulted in failure. Furthermore, as a result of increase in the amount of solid solution of Mn and the like and decrease in the solidus temperature of the fin material, melting of the fin in the brazability test was remarkable, and resulted in failure.

In Comparative Examples 40 to 43, since the components of Zr, Cr, V or Ti in the fin material were excessive, cracks occurred at the time of rolling, and the fin material was not able to be manufactured.

In Comparative Example 44, since the components of Zn in the fin material were excessive, corrosion of the fin material was remarkable in the corrosion resistance test, and resulted in failure.

In Comparative Example 45, since the components of Cu in the fin material were excessive, the sacrificial anode effect of the fin material was insufficient in the corrosion resistance test, and resulted in failure.

In Comparative Example 46, since the components of Mg in the fin material were excessive, the joining ratio was low in the brazability test, and resulted in failure.

INDUSTRIAL APPLICABILITY

The fin material made of an aluminum alloy for heat exchangers of the present invention has excellent material strength at high temperature during braze-heating and excellent buckling resistance during braze-heating. 

1. A fin material made of an aluminum alloy for heat exchangers, the fin material comprising: 1.0 to 2.0 mass % of Mn; 0.7 to 1.4 mass % of Si; and 0.05 to 0.3 mass % of Fe; and one or more kinds of 0.05 to 0.3 mass % of Zr, 0.05 to 0.3 mass % of Cr, and 0.05 to 0.3 mass % of V, with the balance being Al and unavoidable impurities, wherein a number density of intermetallic compounds having a circle-equivalent diameter of 0.025 to 0.4 μm before braze-heating is 3.0×10⁶ particles/mm² or more, an amount of solid solution of Mn is 0.3 mass % or less and a respective amount of solid solution of Zr, Cr, and V is 0.1 mass % or less, and a recrystallization completion temperature during a temperature rise at time of braze-heating is 450° C. or less.
 2. The fin material made of an aluminum alloy for heat exchangers according to claim 1, further comprising one or more kinds of 0.5 to 4.0 mass % of Zn, 0.01 to 0.4 mass % of Cu, 0.01 to 0.3 mass % of Mg, and 0.05 to 0.3 mass % of Ti. 